Prime Minister Boris Johnson has tested positive for the coronavirus and is suffering mild symptoms, the British government said Friday. He is the first leader of a major Western country known to have contracted the virus.

“After experiencing mild symptoms yesterday, the prime minister was tested for coronavirus on the personal advice of England’s chief medical officer, Prof. Chris Whitty,” the government said in a statement. “The test was carried out in No. 10 by NHS staff and the result of the test was positive,” referring to the National Health Service.

In keeping with the guidance, the prime minister is self-isolating in Downing Street.

The government said Johnson would continue to lead the country’s response to the pandemic. But he did not appear at a daily news conference Thursday, at which the chancellor of the Exchequer, Rishi Sunak, rolled out the latest plan to protect workers who have lost wages because of the lockdown of the country.